The proposed research is designed to elucidate the Escherichia coli functions which are necessary for the propagation of bacteriophage lambda and to identify the phage gene products which interact with them. We are using this virus-host interaction system also in order to achieve a better understanding of certain aspects of E. coli physiology. In order to achieve these goals we have developed the necessary techniques for the isolation of E. coli mutants which block lambda DNA replication, RNA transcription and phage head morphogenesis. Emphasis is placed on the characterization of bacterial mutations which, in addition to blocking bacteriophage growth, render the cell itself temperature sensitive for growth. We are in the process of identifying the groP, groN and groE gene products on SDS polyacrylamide gels and purifying the wild-type bacterial gene products by using in vitro assay systems, specifically designed to detect their activities.